I am also curious how old your daughter is. Mine is currently 27 months so I totally understand your concerns & own the same potty seat and booster chair but wow,I can not imagine bringing all the stuff you are thinking of hauling, especially if you will be using bus and/or trams where you'll have to unload and fold the stroller! We live locally and I have been bringing my daughter at least once a month (but usually a lot more) since she was a month old. Obviously packed very differently for different stages of her life but even though we are frequently in a park from open to close (thanks to the neverending parade of out of town guests you get when you live in Orlando!) I have never brought more than our stroller and a mini backpack to use as a diaper bag even when she was teeny tiny.
There are plenty of booster seats available at both restaurants & quick service, however, at 27 months my daughter prefers to sit on her knees on a regular chair at quick service and can reach the tables fine. (I frequently stick her in a high chair anyways only to keep her contained.) The sit downs ask at check in if we want a high chair or booster & have one waiting so she automatically assumes it is her seat when we get to the table & climbs right in. The current high chairs are kind of small so if your child is over 2 and not petite they may not be very comfortable (and if they are over 2 a booster is probably preferable anyways unless they are like my daughter who doesn't sit still well yet once she finishes the little she eats so it is best for everyone if we contain her sometimes but we always start with a booster now & switch to high chair only if need be). The quick service chairs & boosters are as clean as any you'd find at a local family friendly restaurant-not spotless but not disgusting either. I just do a quick wipe down of both chair & eating area with a wipe. (I do still find those placemats that stick on the table very helpful at this stage since she tends to get food all over & the disposable ones are so tiny they take up no space in a diaper bag). I've never used a cover (which would only fit on high chair, not booster) because to me it's just another thing to lug around & you get the same results by just wiping the chair down. (And honestly, I've never experienced this but if you truly felt a chair was really dirty & told somebody at Disney they'd probably bring you another or clean it for you.)
As far as a potty, I'd never bring our Bjorn along either. I have a small, fold up potty seat that sits on top of the potty & folds nicely to fit in its own little bag in our diaper bag. In a pinch I've covered the potty seat with a liner and held her on it. I have never had a problem finding a clean potty for my daughter (who is in the early stages of training so if she needs to go, she needs to go now!). Yes, I've encountered some nasty stalls but never an entire bathroom full & we simply wait for the next potty (I usually wait for the larger stall anyways since it is often me alone & the stroller with her...yes I know they are for handicapped but I will not leave my stroller unattended outside a bathroom, I've known of more than one that has gotten stolen. If it is obvious someone who truly needs the handicapped stall is waiting I would always let them go first but Disney also has companion restrooms available to them in many places, which I will not use).
The baby care centers all have potties in them and they are usually some of the cleanest I've found but with a training toddler they unfortunately aren't always conveniently located.
As far as the laptop, don't bother. Wifi in the parks is okay at best (think of all the people also trying to use it, the more users, the slower it will be!). You can Skype from a smartphone for the same effect but I would focus less on that and more on just enjoying on your own your little one's reactions to things. You can video things to share with family later & that way it is preserved forever.
Hope I helped a little. Seriously, you may think you need to bring so much more for a little one but the less you bring, the better & happier you probably will be after a long day of carting stuff around. If you truly need something you forgot right at that instant baby care probably sells it.
Also, something you seem concerned about that makes you want to bring these things is germs. I hate to tell you this but if your toddler is anything like my 27 month old they will want to touch everything in sight! You can't control this unless you carry them through every single line and hold them in your lap on every single ride. If there's a wall, a chain, a rope, a bar, etc in front of or next to my little one she wants to touch it or run her hands along it! They dont sanitize que lines or ride cars between people. I imagine there are far more germs getting on her that way than from any potty seat or booster/high chair! It would not be a fun day at all for me if I was constantly reminding her not to touch things/put her hands in her mouth. I bring lots of wipes and wipe down her hands and wash at a sink every so often but there is no way I could have a fun day at Disney if I worried about all the germs she is touching nonstop so other than that I just let it go & she's been surprisingly healthy so far.
Have a great trip and try to pack for the parks only what you would bring with you if you were going out and about locally for a day with your toddler.
Toddlers tend to adapt pretty easily to new and different things & if your LO does have a meltdown I doubt it will be over their missing familiar potty chair or booster seat!
. There was a thread about that very thing a couple of weeks ago. I just don't want you to be taken by surprise and upset if it does happen. Prepare some snappy comebacks ahead of time.
